Current Science

Pabitra Nath ¹, Iftak Hussain ¹, Rajib Biswas ¹

Affiliations
1 Applied Photonics and Nanophotonics Laboratory, Department of Physics, Tezpur University, Sonitpur 784 028, IN

Abstract

The working of a robust, long dynamic range, quasicontinuous fibre-optic liquid-level sensor is demonstrated in this communication. The sensor principle is based on periodic evanescent light wave absorption when rising level of liquid gradually replaces the surrounding air medium from a periodically uncladded step-index multimode optical fibre which would cause local variation in normalized frequency parameter (V) of the fibre. With our proposed sensor design, liquidlevel variation as small as 2.5 cm can be measured with high accuracy and repeatability, which can be further enhanced by reducing the spacing between two adjacent regions of the fibre. Owing to its simplicity and robustness in operation, we envision that the proposed sensing technique could emerge as an alternative to the existing optical-based liquid-level sensors.

Keywords

Evanescent Field, Fibre Optic Sensors, Liquidlevel Sensing, Multimode Optical Fibre.

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Dipok K. Bora ¹, Rajib Biswas ²

Affiliations
1 Department of Physics, Diphu Government College, Diphu 782 462, IN
2 Geophysical Lab, Department of Physics, Tezpur University, Tezpur 784 028, IN

Abstract

Of late, there has been a rise in the number of earthquakes in the North East Region (NER) of India. Very recently, a mild tremor shook the East Kameng district of Arunachal Himalaya, when a shallow-depth (16.8 km) earthquake of M_W 5.5 with epicentre 27.707°N and 92.890°E struck at UTC 09 h 22 m 15 s (14 h 52 m 14 s ITC) on 19 July 2019 (refs 1, 2). Importantly, within half an hour two aftershocks were recorded, one in the same epicentral zone of the M_W 5.5 earthquake and another at the southern site of East Kameng district² (Table 1). A M_W 4.9 earthquake was recorded at UTC 22 h 54 m 24 s (04 h 24 m 23 s ITC on 20 July 2019) with epicentre 27.736°N and 92.810°E and depth of 10 km. The highest impact of these earthquakes was felt in the epicentral zone of East Kameng district and in the adjoining regions of Arunachal Pradesh, Guwahati and other parts of Assam and Dimapur, Nagaland. The NER is one of the highly seismically active regions^3,4 and falls in the zone V in the seismic zoning map of India (BIS 2004)⁵. In this context, these felt events are significant because of their epicentral region being located in the NER itself. Figure 1 shows the epicentral plot of the earthquakes and focal mechanism of two earthquakes (from USGS) with prominent tectonic elements of NE India.

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